Radio receiver circuits



May 20, 1952] A. H. A. WYNN RADIO RECEIVER CIRCUITS Filed D80. 14, 1946 INVENTOR ARTHUR H.A.WYNN

.EDUKZU LE OF? ATTORNEY Patented May 20, 1952 burr-so STATES career; critics.

l i-rthur Henry Ashford Wynn; London, England,

"assignorlto A. C; Cossor Limited; Lcnd0n,*Eng-' land;a;-1Bri tish company g I Application December 14, 1946, erial No. 716,2Ql

This invention relatesto radio receivers and more particularly to receivers 1 adapted for reception on aplurality of wave bands. I

=In-a-radio receiver there is at least one variable tuned'circuit, i e. an inductor: and a capacitor in-parallel; one of these reactive elements, usually -th'e capacitor, being variable to permit of the selection of anyone frequency within a certain frequency band. When aireceiver is to be capable ofireceiving on a' plurality of frequency bands, an

alternative or additional reactive; element must beintroduced in each variable .tuned'circuit: thus asecond inductor may replacethe first, or further capacitance may beiintroduced in parallel withathatofcthe variable capacitor. Indetermininglzthelarra'ngementi to be used the designer will Tb guided :by 'theconsideration, inter, alia, thatzaninductor is-usuallyamore expensive componentethan a comparableicapacitor, so that the latter of therabove-suggested methods is likely toebeiadopted; Other considerations, more particularlyinpointswith respectto the present ins ventionfare that a fixed capacitor is a less expensivecomponentthan a semi-fixed (trimmer or preset)-capacitor,' that a preset capacitor of small capacitanceis more practicableof manufacture than one of larger capacitance, and that the capacitance of a tuned circuit decreases as-its frequency increases;

With these'and similar considerationsin mind,

adjustment of the inductor in respect of theone band and after that an adjustment of the semifixed capacitoriin respect of theother band;

Since, as above stated, thelarger capacitance is thatipertaining tothe lower frequency band, it is preferred that-the one bandyi. e.', that using the fixed'capacitor, shall beof lower frequency than therother band, using the. semi-fixed capacitor; By a variable component meant one which can at any time befsetiby the user to any value within :a"; considerable range i and subsequently In Great Britain Decin'bef 20,:1945

4 Claims, (01.- 2505mm 21.. bechangedto-any other-value equal readily, for, thispu'rpose being. accessible from the exterior of thelreceiverduring normal use: by a semifixedi'or'preeset'fcomponent is meant one which is adjustable; perhaps within a small range only, duringlsome. initial lining up process, and is intended toi-remain as; so set thereafter, being therefore usually inaccessible; from the exterior of the receiver during normal use and often requiring the use of: a special tool such as a screwdriver for it's manipulation.

In an embodiment of thel invention as applied to a 'superh'eterodyne receiver having a push button for each of twofrequency ranges there is a single inductor for. the. R; F. tuned circuit and aisingle. inductor for: the local oscillator tuned circuit;'f'similarly there is a single variable capacitor forieach, the two capacitors being ganged in well knownmanner; For thelower frequency range there is afixed capacitor for each tuned circuit and for the higher frequency range there isaapre-set' capacitor for each; these capacitors being switched by the push buttons into or out of circuitxiniparallel with the respective variable capacitor; 1 Theinductors are of pre-set type,-

being=adjustable by;me ans of a variable dustcore.

lining up the receiverfor the, several ranges adefinite procedure :is-followed First the lower frequency push button is, depressed. At some selected spot frequency within the range and selected-spotfrequencywithin this second range andsoine' corresponding selected position'of the ganged variable capacitors the pre-set capacitor isiadjusted until'the circuit is tuned. The local oscillator is dealt with similarly, remembering; that its frequencies, are always to differ from th o se of the R. F. stage by the amount of the intermediate frequency.

The following description relates to the, accompanying drawing which shows a circuit pertaining to one embodiment of the invention.

The circuit shown in the drawing is part of a superheterodyne receiver which, as is well known, requires'provision for variable tuning both in the R. F. stage and in the local oscillator. In the R. F. stage there is a fixed inductor. 3 paralleled by" variable capacitor 5; similarly in the local oscillator circuit there-is a fixed inductor 4 paralleledibyavariable capacitor 6;. There variable 3 capacitors 5 and B are mechanically ganged in well-known manner.

The receiver is intended for reception of two wave bands, being provided with push buttons I and 2 for selection of the band. These push buttons are mechanically interlocked so that only one can be depressed at a time. Suitable mechanical interlocking is represented by the dotted mechanical connection M pivoted at the point Ma. As shown the push button I and associated parts pertain to the higher frequency range, while push button 2 pertains to the lower frequency range. The push buttons I and 2 control the switches II and I2 in the R. F. stage of amplification and the switches I la and I2a in the local oscillator tuning circuit. These switches are all of comparable pattern, the moving elements consisting of L-shaped conductor members I3 which are engageable with contact studs arranged in pairs so that a set of three contact studs can be interconnected at a time. For operation in range A push-button I is moved in the direction of arrow AI which effects movement of the button 2 in the direction of the arrow B2, and for operation in range B, the buttons move in the direction of arrows BI and A2 respectively. As shown in the drawing, the arrangement is set for operation in range A. e

In the R. F. circuit there is a fixed capacitor 7 for use in the lower frequency range and a trimmer capacitor 9 for use in the upper frequency range. Similarly in the local oscillator tuning circuit there is a fixed capacitor 8 for the lower frequency range and a trimmer capacitor ID for the higher frequency range.

The switches are so arranged that when a push button I or 2 is depressed, i. e., moved to the right as in the drawing, the corresponding trimmer or fixed capacitors are put in parallel with the single variable capacitor in that circuit.

In lining up the receiver for the several ranges a definite procedure is followed. First the lower frequency push button is depressed. At some selected spot frequency within the range and some corresponding selected position of the ganged variable capacitors 5 and 6 the R. F. inductor 3 is adjusted to its correct value and then locked in the position as adjusted. Next the higher frequency push button I is depressed (releasing the other mechanically) and at some selected spot frequency within this second range and some corresponding selected position of the ganged variable capacitors 5 and 6 the pre-set capacitor 9 is adjusted until the circuit is tuned. The local oscillator is dealt with similarly, remembering that its frequencies are always to differ from those of the R. F. stage by the amount of the intermediate frequency.

As is well known, single point alignment as above described is more satisfactory with receivers having a small frequency coverage, commonly known as band spread receivers, than it is with receivers in which the frequency band has a large coverage; so that it is with band spread receivers that the invention may be expected to be more useful.

I claim:

1. In a radio receiver for receiving a band of high frequency waves and a band of low frequency waves, a tuned circuit comprising a single pre-set variable inductor whose inductance is variable over only a small range, a single tuning capacitor connected directly in parallel with said inductor and being variable to vary the frequency of said tuned circuit throughout the fre-' quency ranges of both the high frequency band and the low frequency band, switching means having a high frequency band positioned and a low frequency band positioned, a pre-set capacitor whose capacitance is variable over only a small range and being connected in shunt to said inductor by said switching means in the high frequency band position thereof, and a fixed capacitor of greater capacity than said pre-set capacitor connected in shunt to said inductor by said switching means in the low frequency band position thereof.

2. In a radio receiver for receiving a band of high frequency waves and a band of low frequency waves, a tuned circuit comprising a single semi-fixed inductor whose inductance is variable over only a small range, a single variable tuning capacitor connected directly in parallel with said inductor and being variable to vary the frequency of said circuit throughout'the frequency ranges of both said high frequency band and said low frequency band, a fixed capacitor for one of said frequency bands, asemi-fixed capacitor for the other frequency band and having its capacitance variable over only a small range, and a two-position switching means arranged to connect said fixed capacitor and said semi-fixed capacitor alternately in parallel with said inductor, whereby in the process of lining up the tuning of said circuit it is only necessary to make one adjustment for each band, namely, an adjustment of the inductor in respect of one band, and after that an adjustment of the semi-fixed capacitor in respect of the other band.

3. The method of lining up the operation of the tuned circuit specified in claim 1 which comprises placing said switching means in its low frequency band position, setting said tuning capacitor at a predetermined frequency within said low frequency band, adjusting said variable inductor until said circuit is tuned to said predetermined value, shifting said switching means to its high frequency band position, setting said tuning capacitor at a frequency within said high frequency band, and adjusting said pre-set capacitor to tune said circuit to said second-mentioned frequency.

4.. A tuning arrangement for a superheterodyne radio receiver for selectively receiving waves in a high frequency band and in a low frequency band comprising, in combination, a tuned radio frequency receiver circuit and a tuned oscillator circuit, each circuit including a single pre-set variable inductor whose inductance is variable over only a small range, a variable tuning capacitor connected directly in shunt to the inductor in said receiving circuit and being variable to tune said circuit throughout the ranges of said high frequency band and said low frequency band, a variable capacitor connected in shunt with the inductor in said oscillator circuit and being variable to tune said oscillator circuit throughout the appropriate frequency range for said high frequency band and said low frequency band, means connecting said variablecapacitors for ganged operation to maintain a fixed difference in resonant frequency between said receiver and oscillator circuits, switching means having a high frequency band position and a low frequency band position, a pre-set capacitor whose capacitance is variable over only a small range and being connected in shunt to each' of said inductors by said switching means in the high frequency band position thereof, and a fixed capacitor of greater capacity than 'said 5 pre-set capacitor connected in shunt to each of Number said inductors by said switching means in the low 2,065,652 frequency band position thereof. 2,141,756 ARTHUR HENRY ASHFORD WYNN. 2,148,633 5 2,209,959 REFERENCES CITED 2 301,934 The following references are of record in the 2,354,14 file of this patent: 2,434,299 UNITED STATES PATENTS 2538438 10 2,538,439 Number Name Date 1,658,718 Hardcastie Feb. 7, 1928 1,992,805 Becker "Feb. 26, 1935 2,029,461 Brush Feb. 4, 1936 6 Name Date Carlson Dec. 29, 1936 Linsell Dec. 27, 1938 MacDonald Feb. 28, 1939 Chittick Aug. 6, 1940 Edwards Nov. 17, 1942 Shaw July 18, 1944 Van Loon Jan. 13, 1948 Bedford et a1 Jan. 16, 1951 Bedford et a1 Jan. 16, 1951 OTHER REFERENCES Automatic Tuning Devices, Radio News, April, 1939, by Queen, (page 17). 

